This invention relates to an electroconductive or electrical contact (which will simply be referred to as xe2x80x9ccontactxe2x80x9d) to be brought into contact with an electrical terminal member such as terminal plate, flat lead, ball contact or another electrical contact for establishing electrical connector therebetween, and in particular, to a surface structure of a contacting portion of such a contact and a method for producing the contact.
in order to establish a removable electrical connection between two electrical units, it is known in the prior art that one of them has contacts which are brought into contact with corresponding terminal members of the other unit, respectively. Typically, one unit is an electrical connector and the other unit is a circuit component part, a printed circuit board, an IC package or other electrical units.
It is also known in the prior art that the electrical connection between the contact of one unit and the terminal member of the other unit is often made insufficient due to presence of oxide or any contaminant attached to the surfaces of the contact and the terminal member. In order to achieve reliable electrical connection, such oxide or contaminant must be removed to expose metal surfaces of the contact and the terminal member when they are brought into contact with each other.
in order to remove the oxide or contaminant, it is known in the art to apply contacting pressure on the order of 1N (newton) per contact to crush the oxide or the contaminant. If one unit is an electrical connector having 100 contacts, the contacting pressure is required the order of 100N in total. Such a large contacting pressure undesirably makes it difficult to establish an electrical connection between the two units.
For example, when a liquid crystal display (hereinafter abbreviated to LCD) panel is connected to a connector, that is a so called LCD connector, mounted on a printed circuit board, an indium tin oxide (hereinafter abbreviated to ITO) film as a transparent conductive electrode is used between the LCD panel and the LCD connector. When the ITO film are applied with high contacting pressure from the contact, it may result in a damage or a breakage.
in another example where the unit connected to the connector is a unit having a ball grid array (BGA) as the terminal members, for example, a semiconductor BGA package such as an LSI package or an IC package, the balls made of solder in the BGA may be undesiredly broken or released under the high contacting pressure. In this event, troublesome repair work is required.
Another known approach for removing the oxide and/or contamination is to relatively slide the both units to be connected to thereby wipe off the oxide and/or contamination. However, considering miniaturization of electronic devices, it becomes difficult to relatively slide the units to be connected to each other in the small-size device.
It is an object of this invention to provide an electrical contact which assures reliable connection with a terminal member under a low contacting pressure without interference of oxide and/or contamination adhered thereto.
It is another object of this invention to provide a method of forming the above-mentioned contact.
This invention provides an electrical contact having a contacting portion to be brought into contact with and electrically connected with a terminal member which comprises a conductive body having a body surface, a conductive surface coating layer formed on the body surface of at least the contacting portion, and hard conductive particles dispersed in the surface coating layer. The surface coating layer has an irregular surface due to presence of the hard conductive particles dispersed therein.
A particle size of the hard conductive particles must be selected so that the conductive surface coating layer has an irregular surface due to presence of the hard conducive particles dispersed or embedded in the conductive surface coating layer. When the particle size is excessively small in comparison with a thickness of the conductive surface coating layer, the conductive surface coating layer results to have the irregular surface. When the particle size is excessively large in comparison with a thickness of the conductive surface coating layer, the conductive surface coating layer cannot firmly retain the hard conductive particles therein. The hard conductive particles preferably have an average particle size around the thickness size of the conductive surface coating layer. Typically, the particle size is about 0.3-2, preferably, 0.5-1.5 times of the thickness size of the conductive surface coating layer.
The surface coating layer is typically a plated metal layer having the hard conductive particles.
The plated metal layer may comprise a first plated sub-layer containing conductive hard particles dispersed therein and formed on the body surface, and a second plated sub-layer formed on the first plated sub-layer.
The first plated sub-layer may comprise a primary plated sub-layer made of a first metal and containing the conductive hard particles dispersed therein, and a secondary plated sub-layer made of the first metal and formed on the primary plated sub-layer. The second plated sub-layer is made of a second metal different from the first metal and formed on the secondary plated sub-layer.
The conductive body is made of elastic metal such as phosphor bronze, or other Cu-base alloy.
The first metal is one selected form a group of Ni, Cu, and Sn.
The second metal is one selected from a group of Au, Au-alloy, Pd. Pdxe2x80x94Ni alloy, Sn and Snxe2x80x94Pb alloy.
The hard conductive particles are particles made of one or more selected from a group of TiN, WC, Ni, TiO2 and Cr2O3.
The contact can be produced by the following method.
A blank is prepared by blanking or stamping a sheet of conductive elastic plate. The blank comprises a carrier frame and a plurality of contact blanks extending from the carrier frame to their extending free ends in parallel with each other. While, an electroplating bath is prepared which contains a composite plating solution comprising an electroplating solution of a first metal acid and hard conductive particles suspended therein. The blank is supported in the electroplating bath by holding the carrier above the composite plating solution so that the contact blanks are at least partially dipped in the composite plating solution, and then subjected to an electroplating process. By the electroplating process, a first plated layer of the first metal is formed on a surface of a portion of each of the contact blanks dipped in the composite plating solution and, simultaneously, the hard conductive particles are deposited on the surface due to electro-deposition so that the hard conductive particles are dispersed in the first plated layer. The first plated layer has an outer surface with irregularity due to presence of the hard conductive particles dispersed therein. Then, each of the contact blanks is separated or cut from the carrier frame to provide the contact.
Before and/or after being cut, each of the contact blanks can be formed in a desired shape by bending and/or curving process.
Before cutting each of contact blanks from the carrier frame, the blank can be subjected to second and/or third plating process to form second and/or third plated layer on the first plated layer. The second plated layer is of the first metal and is directly formed on the first plated layer by use of a second electroplating bath containing the electroplating solution of the first metal acid without the hard conductive particles. Alternatively, the third plated layer is of a second metal add different from the first metal and is directly formed on the first plated layer by use of a third electroplating bath containing the electroplating solution of the third metal acid without the hard conductive particles. When the both of the second and third plated layers are formed, the third plated layer is directly formed on the second plated layer.
This invention further provides an electrical connector having a plurality of contacts for establishing electrical connection between two electric objects each having a plurality of terminal members. Each of the contacts is the contact according to this invention as described above and has two contacting portions at opposite ends thereof so as to be brought into contact with terminal members of the two electric objects.